{-# LANGUAGE TemplateHaskell #-}

import TestMod

f :: Int
f = $$(foo)

main :: IO ()
main = main

{-# LANGUAGE ScopedTypeVariables #-}
{-# LANGUAGE TemplateHaskell #-}
{-# LANGUAGE TypeApplications #-}

module TestMod where

import Language.Haskell.TH.Syntax (Q, TExp)

get :: forall a. Int
get = 1

foo :: forall a. Q (TExp Int)
foo = [|| get @a ||]

Test.hs:6:8: error:
    • The exact Name ‘a’ is not in scope
        Probable cause: you used a unique Template Haskell name (NameU),
        perhaps via newName, but did not bind it
        If that's it, then -ddump-splices might be useful
    • In the result of the splice:
        $foo
      To see what the splice expanded to, use -ddump-splices
      In the Template Haskell splice $$(foo)
      In the expression: $$(foo)
  |
6 | f = $$(foo)
  |        ^^^

Test.hs:6:8: error:
    • GHC internal error: ‘a’ is not in scope during type checking, but it passed the renamer
      tcl_env of environment: [r3Kl :-> Identifier[f::Int, TopLevelLet [] True],
                               r3PI :-> Identifier[main::IO (), TopLevelLet [r3PI :-> main] True]]
    • In the type ‘a’
      In the expression: get @a
      In the result of the splice:
        $foo
      To see what the splice expanded to, use -ddump-splices
  |
6 | f = $$(foo)
  |